ABSTRACT
If we recall that linear systems are those to which the principle of superposition applies, then from the fact that, as we saw in Chapter 2, any reasonably well-behaved excitation function can be written as the sum, series or integral of simple functions – and, frequently, harmonic functions – it follows that the system’s response is the sum, series or integral of the individual harmonic responses. In principle, therefore, to consider nonharmonic excitations may seem to be only a complication of a computational nature rather than something that provides further physical insight into the behaviour of linear systems. However, even if there is some truth in this, things are not so simple. Different approaches – and, accordingly, different methods and techniques – are in fact available to the analyst, and each one of them, guratively speaking, sheds light from a different angle on the fundamental aspects of the problem.
